The following are teacher/Principal approved websites, suitable for students in 2nd through 6th Grade:

American West - Pony Express Information
A Plus Math
Belle Plaine Public Schools! 2/3/4/5/6
Ben's Guide 4
California Mission Studies Assn 4
California Missions 4
Compass Learning 2/3/4/5/6
Cool Math 2/3/5/6
Dictionary 5/6
Discovery Kids 6
Dr. Seuss
Enchanted Learning 5
Fact Monster 2/3
First in Math  2/3/4/5/6
Funbrain
Grolier BookFlix 2/3
History Central 6
I Know That
Magic Keys 2/3/5
McGraw Hill Glencoe 5
Multiplication 2/3/4
National Geographic for Kids 6
National Geographic 6
PBS 5
Practice Math Tests
Read Write Think Comics 2/3/4
Read Write Think
San Diego Union Tribune 5
San Diego Zoo
Scholastic Kids
School House
Science News for Kids
Sea World
Senselang
Starfall
Wikipedia 5/6/7/8
Wild Animal Park
Wordly Wise 4/5
Zingy Learning 4/5/6